Economists said the figures, which showed a 2.1% decline in exports, were a worrying sign that the slowdown in the world economy would restrict growth in British exports.

The trade balance narrowed to £4.6bn after an even bigger drop in imports during the month. Britain's goods trade gap with the rest of the world narrowed to £8.23bn in August, broadly in line with expectations.

Howard Archer, chief European and UK economist at IHS Global Insight, said: "Signs of net trade riding to the rescue of the UK economy remain conspicuous by their absence."

Disappointingly for the government, while exports to the eurozone increased by 1.3%, exports to non-EU countries dropped by 4.9%.

The UK deficit compares with a $20bn (£12.7bn) surplus in Chinese net trade for August and $104bn surplus this year. India is running a $59bn surplus this year, while the eurozone countries have managed a $2.2bn surplus, largely on the back of German exports to the far east.

Commenting on the UK trade figures, David Kern, chief economist at the British Chambers of Commerce, said: "It is disappointing that exports fell slightly, but imports fell even more, and overall the result was an improvement in the net trade position.

"While this is positive, the improvement this year is by no means sufficient, and it is critical that the relatively strong manufacturing figures we have seen recently should be translated into a much stronger trading position.

He warned ministers to support exports with short-term trade finance or risk losing out further in fast-growing markets such as China, India and Brazil."

Andrew Goodwin, economic adviser to the Ernst & Young Item Club, said the winter months were unlikely to provide exporters with the lift they wanted.

"Most worrying is further evidence that exports are levelling off, having recovered strongly over the first half of the year," he said. "This is consistent with the weaker data on export orders from recent business surveys and reflects a softening in global demand. There has been a notable drop-off in demand from our key export market, the European Union.

"We appear to be entering a soft patch for global growth, with major question marks over short-term growth prospects in both the US and eurozone. We expect these to be overcome but only after a period of subdued growth through the winter."

Britain's trade deficit widened to a post-war record in July after a surge in imports. Figures for imports showed a £4.9bn deficit, taking the quarterly figure to £13.2bn in the three months to July – the largest deficit since annual records began in 1946.